1. Technical Field
The present invention relates to a fuel supply method and a fuel supply system and, more specifically, to a fuel supply method and fuel supply system for supplying fuel in a fuel injection device of a gas turbine so as to achieve low-NOx operation.
2. Description of the Related Art
There has been a demand in recent years for a fuel injection nozzle for combustors, capable of injecting fuel such that the exhaust gas has a low NOx concentration, owing to the recent progressively growing severity of controls concerning NOx emission imposed on aero and industrial combustors. To achieve low-NOx combustion, the fuel injection nozzle is required to inject fuel such that the mean flame temperature is low and temperature distribution in flames is uniform. Fuel must be mixed with a large amount of air to lower the mean flame temperature and to make temperature distribution in flames uniform.
When fuel is jetted by a conventional fuel injection nozzle N having a single fuel passage 101 as shown in FIG. 3, the fuel is mixed in a large amount of air for low-NOx combustion, the spatial distribution of the fuel is liable to occur, and flame temperature is distributed. Such a mode of combustion is undesirable to reduce NOx emission. Although no problem arises in combustion while the combustor is operating in a high power setting, the air-fuel mixture becomes excessively lean and combustion becomes unstable while the combustor is operating in a low-power or middle-power settings.
Unstable combustion that occurs in the low-power setting or middle-power setting may be avoided by an improved fuel injection nozzle obtained by altering the conventional fuel injection nozzle N. The improved fuel injection nozzle has a plurality of series of swirl vanes which are concentrically arranged in different radial positions, and a plurality of series of fuel injection mechanisms which are concentrically arranged in different radial positions. The operation of the fuel injection mechanisms is regulated according to engine power settings, and the amount of air into which the fuel is mixed is regulated for the so-called staging combustion. A fuel injection device provided with such fuel injection mechanisms is under development.
When the plurality of fuel injection mechanisms in different radial positions are used for staging combustion, problems arises in holding the fuel injection mechanisms and in a method of supplying fuel to the fuel injection mechanisms.
For example, if the fuel injection mechanisms are held individually on holding arms and the fuel is supplied through the arms, blockage of the air flow into combustor increases, and the air flowing into a fuel injection unit will be distorted. There is the possibility that joints of the fuel injection mechanisms and the arms are damaged due to difference in thermal expansion between the fuel injection mechanisms and the arms.